Field of the Invention
The invention concerns a scanning device for semiconductor wafers for the preparation of a surface analysis in which a liquid drop is moved over the surface of the semiconductor wafer for determining a concentration of metal and dopant traces in the liquid drop.
Such scanning devices are used to collect metal and dopant traces from the surface of the semiconductor wafer and ascertain the purity of the surface of the semiconductor wafer. On the basis of the result of the analysis, the preceding processing steps can then be assessed.
In preparation for scanning, the semiconductor wafer is firstly treated in a gas-phase treatment chamber, a so-called vapor phase decomposition (VPD) box with a hydrogen fluoride gas. The semiconductor wafer is subsequently removed from the VPD box and a liquid drop is placed on the now hydrophobic surface of the semiconductor wafer. The semiconductor wafer itself is held manually with the aid of a suction pipette. The liquid drop is then rolled over the surface of the semiconductor wafer by carefully tilting the latter. As this occurs, metal and dopant traces are collected from the surface of the semiconductor wafer and concentrated in the liquid drop.
While the treatment step in the VPD box necessary before scanning the semiconductor wafer is to be regarded as a very simple and reliable process, scanning the semiconductor wafer manually requires considerable dexterity and practice. At the same time, the liquid drop must be prevented from rolling off the semiconductor wafer, which would make an analysis impossible. In addition, when scanning the semiconductor wafer, it must be ensured that all the regions of the surface of the semiconductor wafer are covered.
In the case of relatively small semiconductor wafers, this freehand scanning is to be regarded as an entirely customary practice. However, in the case of semiconductor wafers with a diameter of 300 mm, this freehand scanning becomes extremely difficult or impossible.
Therefore, for the scanning of such semiconductor wafers, devices that carry out both the VPD treatment and the scanning of the surface of the semiconductor wafers fully automatically have been developed. Such devices are, however, extremely cost-intensive and unsatisfactory in their reliability. This applies in particular to the scanning of semiconductor wafers that are difficult to scan, such as semiconductor wafers with LPCVD nitride layers.
Furthermore, it may happen that, during scanning, parts of the liquid drop remain on the surface of the semiconductor wafer, in other words are lost. These lost amounts of liquid can be collected again when scanning manually, whereas this recollection is not possible in the case of fully automatic devices.